The number four is the only number in the English language that is spelled with the same number of letters as the number itself.

Forty is the only number with all its letters in alphabetical order, and one is the only number to have its letters in reverse alphabetical order.

Twenty-nine is the only number that is written with as many strokes as its numerical value (if Y is written with three strokes).

The number 172 can be found on the back of the five-dollar bill in the bushes at the base of the Lincoln Memorial.

A pound of gold actually weighs less than a pound of feathers. The reason is that feathers are measured in avoirdupois weight in which there are 16 ounces per pound. Gold is measured in troy weight with 12 ounces per pound.